A new synthesis of functionalized 2,2-biimidazoles

Article abstract of DOI:10.1055/s-0029-1218655

A new two-step synthesis of N,N-disubstituted 2,2-biimidazoles from bisimidoyl chlorides is reported. The bisimidoyl chlorides react smoothly with (2,2-dimethoxyethyl)amine to give bisamidines that are subsequently cyclized to give the corresponding biimidazoles. Georg Thieme Verlag Stuttgart New York.

Full text of DOI:10.1055/s-0029-1218655

PAPER
1311
A New Synthesis of Functionalized 2,2¢-Biimidazoles
F
unctionalized 2,2
e
¢
-
Biimidazo
v
les in Stippich,a Robert Kretschmer,a Rainer Beckert,*a Helmar Goerlsb
a
Institute of Organic and Macromolecular Chemistry, Humboldtstr. 10, 07743 Jena, Germany
Institute of Inorganic and Analytical Chemistry, August-Bebel-Str. 2, 07743 Jena, Germany
Fax +493641948212; E-mail: Rainer.Beckert@uni-jena.de
b
Received 12 November 2009; revised 15 December 2009
undergo prototropic rearrangements.10 Consequently,
their aminolysis reaction with amines that possess an ad-
ditional electrophilic substructure (in this case, aminoacet-
aldehyde acetals) should lead to functionalized amidines
2. Upon activation, the latter should be capable of cycliz-
ing intramolecularly via their prototropic form 2¢ to final-
ly yield the desired 1,1-bisaryl-2,2¢-biimidazoles 3.
Alternatively, a criss-cross cyclization could occur to give
the ring-fused products 4, but this was not observed
(Scheme 1).
Abstract: A new two-step synthesis of N,N¢-disubstituted 2,2¢-bi-
imidazoles from bisimidoyl chlorides is reported. The bisimidoyl
chlorides react smoothly with (2,2-dimethoxyethyl)amine to give
bisamidines that are subsequently cyclized to give the correspond-
ing biimidazoles.
Key words: acetals, biimidazole, heterocycles, cyclization, diaza-
diene complexes
2,2¢-Biimidazoles represent a well-established class of
heterocycles and they are of interest as ligands for the for-
mation of metal complexes,1 as sensors for anions,2 as
building blocks for supramolecular architectures,3 as sen-
sitizers,4 and as biologically active derivatives.5 In addi-
tion, bridged derivatives of biimidazole and their benzo
analogues have often been used in studies on the forma-
tion and dimerization of nucleophilic carbenes.6
Ar
N
MeO
MeO
Ar
H2NCH(OMe)2
toluene, Et3N
Cl
N
NH
Ar
OMe
OMe
HN
N
Cl
N
Ar
1a–d
2a–d
Ar
Starting from glyoxal and its derivatives or from cyano-
gen, only 2,2¢-biimidazoles that are unsubstituted at the
nitrogen atoms are accessible,7 and N-alkylated or N-ary-
lated derivatives are rather rare. The approach most com-
monly used for generating highly substituted derivatives
of 2,2¢-biimidazole involves transition metal-mediated
homocoupling strategies.2,3 2,2¢-Biimidazole itself can be
transformed (e.g., by N-benzylation) to produce materials
that are soluble in organic solvents and can therefore be
further functionalized.8
MeO
MeO
Ar NH
N
N
OMe
OMe
HCOOH
N
N
N
N
HN Ar
Ar
3a–d
Ar
2'a–d
N
N
1–3a: Ar = 4-tolyl
b: Ar = 4-BrC6H4
c: Ar = 3-F3CC6H4
d: Ar = 4-MeOC6H4
N
N
Ar
Our aim, therefore, was to develop a short and efficient
route to derivatives based on C2 building blocks such as
bisimidoyl chlorides 1 derived from oxalic acid. These
easily accessible compounds are distinguished by their
well-defined electrophilicity, which lies between that of
typical acyl chlorides and that of reactive alkyl halides.
This permits selective reactions that often initiate cascade
reactions. For example, N-methylimidazole reacts with
bisimidoyl chlorides derived from oxalic acid to give bis-
cationic tricyclic systems, for example diimidazo[1,2-
a:2¢,1¢-c]pyrazines.9 As part of our ongoing studies in the
area of multifunctional ligand synthesis, we report our re-
sults on the cyclization reactions of bis-electrophilic
building blocks 1 with (2,2-dimethoxyethyl)amine.
4 not observed
Scheme 1 Synthesis of amidines 2 and their subsequent cyclization
to biimidazoles 3
The bisimidoyl chlorides 1 were synthesized by using
known procedures.10,11 Aminolysis of compounds 1 was
carried out in triethylamine–toluene by heating under re-
flux to give the bisamidines 2 in yields of up to 70%. This
procedure turned out to be easy and fast. Moisture and air
were tolerated. Monitoring by thin-layer chromatography
showed complete consumption of the starting materials
after only 10 minutes or 60 minutes in the case of electron-
donor- or electron-acceptor-substituted aryl moieties in 1,
respectively. The bisamidines 2 were obtained as slightly
yellow compounds, which are readily soluble in common
organic solvents.
The products of the reaction of derivatives 1 with nucleo-
philes are often characterized by their distinct tendency to
SYNTHESIS 2010, No. 8, pp 1311–1314
Advanced online publication: 29.01.2010
DOI: 10.1055/s-0029-1218655; Art ID: T21909SS
© Georg Thieme Verlag Stuttgart · New York
x
x
.
x
x
.2
0
1
0
Elemental analyses and mass spectral studies confirmed
the presence of a 2:1 acylation product 2. Because these
molecules show strong prototropism, the NMR spectra

1312
K. Stippich et al.
PAPER
displayed only broad and poorly resolved signals in chlo-
roform-d; the resolution was improved in dimethyl sulf-
oxide-d6, which allowed the assignment of the key
signals.
On heating in refluxing formic acid for 30 minutes, com-
pounds 2 underwent cyclization in nearly quantitative
yields. All the products were fully characterized by means
of elemental analyses, mass spectroscopy, and NMR
spectroscopy. However, these techniques were unable to
distinguish between products 3 and 4. A single-crystal X-
ray analysis of 3b allowed an unambiguous structural as-
signment of the structure of this compound, as shown in
Figure 1. Therefore, the cyclization products of 2a–d have
the structures of the N,N¢-diaryl-2,2¢-biimidazoles 3.
Figure 2 ORTEP plot (50% probability ellipsoids) of the solid-state
molecular structure of complex 5. Selected bond lengths in Å: Mo1a–
N1a 2.278(2), Mo1a–N1ai 2,278(2), N1a–C1a 1.329(4), N1a–C2a
1.372(4), N1ai–C1ai 1.329(4), N1ai–C2ai 1.374(3), C1a–C1ai
1.456(5), C1a–N2a 1.353(4), C1ai–N2ai 1.355(4), Mo1a–C12a
2.033(3), Mo1a–C11a 1.947(3), Mo1a–C12ai 2.033(3), Mo1a–C11ai
1.947(3)
tion of the bisamidines 2. The products were obtained eas-
ily and rapidly and in good overall yields. The newly
synthesized 2,2¢-biimidazoles are readily soluble in com-
mon organic solvents and, as exemplified by derivative
3b, have suitable structural features for subsequent cross-
coupling by various methods. Whereas the diazadiene
subunit in compounds 3 has an s-trans arrangement, the
complexation reaction with reactive molybdenum carbon-
yl allowed the synthesis of a typical s-cis-diazadiene met-
al complex 5.
Figure 1 ORTEP plot (50% probability ellipsoids) of the solid-state
molecular structure of biimidazole 3b. Selected bond lengths (Å):
N1–C6 1.424(3), N1–C7 1.384(4), N1–C9 1.373(3), N2–C8 1.373(3),
N2–C9 1.315(3), C9–C10 1.469(3), N3–C10 1.313(3), N3–C11
1.378(3), N4–C10 1.371(3), N4–C12 1.381(3), N4–C13 1.431(3),
C7–C8 1.343(4), C11–C12 1.359(4)
All reagents and solvents were obtained from commercial sources
and were used without further purification. Compounds 1a–d were
synthesized according to the methods reported in the literature.10
1
The H- and 13C NMR-spectra were recorded on a Bruker Avance
250 spectrometer; shifts are given in ppm relative to the signals of
the solvent. Melting points were measured on a Krüss KSPS 1000
and are uncorrected. IR spectra were measured on a Bio-Rad FTS-
25. Mass spectroscopy was carried out on a Fison Trio 200. Elemen-
All bond lengths and angles of 3b were in the expected
ranges. The compound may be of considerable interest,
since the presence of a bromo substituent should permit tal analyses were performed on a Leco CHNS-932. Merck silica gel
60 (0.040–0.063 mm) was used for column chromatography.
further functionalization reactions, e.g. by metal-mediated
cross-coupling reactions.
Condensation of Biimidoyl Chlorides 1a–d with (2,2-Dimeth-
Because 2,2¢-biimidazoles are well known to form metal
complexes, we attempted the preparation of a molybde-
num(0) complex from tetracarbonyl(norbornadiene)mo-
lybdenum(0) and the biimidazole 3a in toluene.
Compound 5 was obtained as yellow crystals in 83%
yield. The results of an X-ray crystallographic analysis of
this complex are shown in Figure 2.
oxyethyl)amine; General Procedure
Bisimidoyl chloride 1a–d (3.3 mmol) was dissolved in toluene (25
mL) at r.t. (MeO)2CHCH2NH2 (0.69 mL, 6.0 mmol) and Et3N (1.6
mL, 12 mmol) were added, and the resulting yellow mixture was re-
fluxed for 10–60 min. The soln was cooled to r.t., and the precipitate
was filtered off and washed with toluene (10 mL). The filtrates were
combined and the solvent was removed in vacuo. The resulting oil
or solid was purified by recrystallization or column chromatogra-
phy.
The biimidazole moiety is twisted around the C1a–C1a¢-
axis by about 20°; this may be due to steric hindrance be-
tween the two tolyl substituents. The aromatic rings of
these tolyl groups are twisted by about 60° each with re-
spect to the imidazole moiety. The bond lengths of the
complex lie in the expected range, and are shown in
Figure 2.
N1,N2-Bis(2,2-dimethoxyethyl)-N¢1,N¢2-bis(4-methylphe-
nyl)ethanediimidamide (2a)
Reaction time: 1 h. The resulting orange oil was crystallized (hep-
tane) to give a colorless solid; yield: 47%; mp 98.5–99.2 °C.
IR (ATR): 3310, 2892, 1634, 1487, 1257, 1125, 1041, 881, 787
cm–1.
1H NMR (250 MHz, CDCl3): d = 2.17 (s, 6 H, CH3), 3.24 (s, 12 H,
To sum up, a series of new 2,2¢-biimidazoles 3a–d were
obtained starting from bisimidoyl chlorides 1 by reaction OCH3), 3.60 (br s, 4 H, CH2), 4.27 (br s, 2 H, CH), 6.39–6.96 (br s,
8 H, aryl-H).
with (2,2-dimethoxyethyl)amine and subsequent cycliza-
Synthesis 2010, No. 8, 1311–1314 © Thieme Stuttgart · New York

PAPER
Functionalized 2,2¢-Biimidazoles
1313
13C NMR (63 MHz, CDCl3): d = 20.5, 45.2, 53.8, 101.9, 121.3,
128.8, 132.1, 145.5, 151.3.
1,1¢-Bis(4-methylphenyl)-1H,1¢H-2,2¢-biimidazole (3a)
Beige solid; yield: 67%; mp 132.7–133.0 °C.
MS (EI): m/z (%) = 443 (100), 442 (86), 367 (41), 189 (52), 131
IR (ATR): 1513, 1417, 1303, 1080, 963, 819, 741, 724 cm–1.
(57), 75 (64).
1H NMR (250 MHz, CDCl3): d = 2.31 (s, 6 H, Aryl-CH3), 6.68 (d,
J = 8.3 Hz, 4 H, aryl-H), 6.98 (d, J = 8.3 Hz, 4 H, aryl-H), 7.03 (d,
J = 1.0 Hz, 2 H, imidazole-H), 7.21 (d, J = 1.0 Hz, 2 H, imidazole-
H).
13C NMR (63 MHz, CDCl3): d = 21.0, 121.3, 124.0, 129.5, 129.6,
134.7, 137.4, 137.6.
Anal. Calcd for C24H34N4O4: C, 65.14; H, 7.74; N, 12.66. Found: C,
65.19; H, 7.83; N, 12.64.
N¢1,N¢2-Bis(4-bromophenyl)-N1,N2-bis(2,2-dimethoxyeth-
yl)ethanediimidamide (2b)
Reaction time: 10 min. The resulting solid was crystallized (t-
BuOMe) to give a colorless solid; yield: 62%; mp 104.8 °C.
MS (EI): m/z (%) = 315 (18), 314 (66), 313 (100), 223 (16), 91 (11).
Anal Calcd for C20H18N4: C, 76.41; H, 5.77; N, 17.82. Found: C,
75.97; H, 5.62; N, 17.79.
IR (ATR): 3288, 2936, 1613, 1481, 1193, 1118, 1050, 829, 814
cm–1.
1H NMR (250 MHz, CDCl3): d = 3.34 (s, 12 H, OCH3), 3.40 (br s,
1,1¢-Bis(4-bromophenyl)-1H,1¢H-2,2¢-biimidazole (3b)
From bisamidine 2b (2.0 mmol) in HCO2H (5 mL); beige solid;
yield: 90%; mp 203.2–203.6 °C.
IR (ATR): 1487, 1424, 1300, 1065, 960, 830, 738, 717 cm–1.
4 H, CH2), 4.37 (br s, 2 H, CH), 6.39–7.32 (br s, 8 H, aryl-H).
13C NMR (63 MHz, CDCl3): d = 42.5, 54.2, 101.9, 115.7, 123.2,
131.4, 147.6, 150.2.
MS (EI): m/z (%) = 572 (15), 497 (14), 255 (15), 197 (13), 171 (20),
75 (100)
1H NMR (250 MHz, CDCl3): d = 6.71 (d, J = 8.8 Hz, 4 H, aryl-H),
7.06 (d, J = 1.3 Hz, 2 H, imidazole-H), 7.25 (d, J = 1.3 Hz, 2 H,
imidazole-H), 7.36 (d, J = 8.8 Hz, 4 H, aryl-H).
13C NMR (63 Hz, CDCl3): d = 121.3, 121.6, 125.8, 130.2, 132.3,
136.1, 137.1.
Anal. Calcd for C22H28Br2N4O4: C, 46.17; H, 4.93; N, 9.79; Br,
27.92. Found: C, 46.13; H, 4.94; N, 9.51; Br, 27.71.
N1,N2-Bis(2,2-dimethoxyethyl)-N¢1,N¢2-bis[3-(trifluorometh-
yl)phenyl]ethanediimidamide (2c)
Reaction time: 10 min. The resulting orange-brown oil was purified
by column chromatography [silica gel, heptane–EtOAc (2:1)];
yield: 60%; colorless solid; mp 84.6–87.0 °C.
MS (EI): m/z (%) = 445 (62), 444 (66), 443 (100), 287 (18), 181
(34), 155 (22).
Anal. Calcd for C18H12Br2N4: C, 48.68; H, 2.72; N, 12.62; Br, 35.98.
Found: C, 48.38; H, 2.85; N, 12.26; Br, 36.42.
IR (ATR): 3380, 2933, 1641, 1523, 1329, 1113, 1069, 797, 699
cm–1.
1H NMR (250 MHz, CDCl3): d = 3.42 (s, 12 H, OCH3), 3.52 (br s,
4 H, CH2), 4.49 (br s, 2 H, CH), 6.54–7.39 (br s, 8 H, aryl-H).
13C NMR (63 MHz, CDCl3): d = 42.4, 54.3, 101.9, 118.3, 119.3,
124.1, 124.7, 128.8, 130.7, 148.7, 150.3.
1,1¢-Bis[(3-trifluoromethyl)phenyl]-1H,1¢H-2,2¢-biimidazole
(3c)
Beige solid; yield: 96%; mp 206.7–207.7 °C.
IR (ATR): 102, 1496, 1473, 1461, 1326, 1289, 1166, 1115, 1066,
980, 893, 783, 629 cm–1.
1H NMR (250 MHz, CDCl3): d = 6.97–7.02 (m, 4 H, aryl-H), 7.13
(d, J = 1.1 Hz, 2 H, imidazole–H), 7.32 (d, J = 1.1 Hz, 2 H, imida-
zole-H), 7.35 (d, J = 8.0 Hz, 2 H, aryl-H), 7.51 (d, J = 8.0 Hz, 2 H,
aryl-H).
MS (EI): m/z (%) = 551 (19), 550 (23), 443 (16), 243 (22), 145 (12),
75 (100).
Anal Calcd for C24H28F6N4O4: C, 52.36; H, 5.13; N, 10.18. Found:
C, 52.79; H, 4.87; N, 9.94.
13C NMR (63 MHz, CDCl3): d = 120.8, 121.1, 124.4, 125.2, 127.1,
129.9, 130.7, 131.2, 137.0, 137.4.
N1,N2-Bis(2,2-dimethoxyethyl)-N¢1,N¢2-bis(4-methoxyphe-
nyl)ethanediimidamide (2d)
Reaction time: 1 h. The resulting brown oil was purified by column
chromatography [silica gel, CH2Cl2–MeOH (95:5)] to give a brown
syrup; yield: 16%.
MS (EI): m/z (%) = 423 (44), 422 (100), 421 (86), 277 (31), 262
(22), 145 (22).
Anal. Calcd for C20H12F6N4: C, 56.88; H, 2.86; N, 13.27. Found: C,
57.12; H, 2.95; N, 13.56.
IR (ATR): 3369, 2936, 1610, 1498, 1235, 1124, 1068, 1031, 826
cm–1.
1H NMR (250 MHz, CDCl3): d = 3.32 (s, 12 H, OCH3) 3.41 (br s, 4
H, CH2), 3.76 (s, 6 H, Ar-OCH3), 4.34 (br s, 2 H, CH), 6.61–7.00 (br
s, 8 H, aryl-H).
13C NMR (63 MHz, CDCl3): d = 42.5, 54.0, 55.5, 102.1, 113.9,
122.3, 142.0, 150.6, 155.6.
1,1¢-Bis(4-methoxyphenyl)-1H,1¢H-2,2¢-biimidazole (3d)
From bisamidine 2d (0.67 mmol) in HCO2H (3 mL); beige solid;
yield: 82%; mp 190.5–190.9 °C (dec).
IR (ATR): 1514, 1466, 1300, 1251, 1188, 1108, 1026, 853, 747, 710
cm–1.
1H NMR (250 MHz, CDCl3): d = 3.77 (s, 6 H, OCH3), 6.71 (m, 8 H,
aryl-H), 7.01 (d, J = 1.0 Hz, 2 H, imidazole-H), 7.21 (d, J = 1.0 Hz,
2 H, imidazole-H).
13C NMR (63 MHz, CDCl3): d = 55.5, 114.1, 121.5, 125.4, 129.5,
130.3, 137.7, 158.8.
MS (EI): m/z (%) = 475 (58), 474 (100), 399 (57), 306 (35), 205
(62), 147 (100).
Anal. Calcd for C24H34N4O6: C, 60.74; H, 7.22; N, 11.81. Found: C,
60.73; H, 7.23; N, 11.70.
MS (EI): m/z (%) = 346 (56), 345 (100), 239 (16), 224 (12), 173
(10), 77 (6).
Cyclization to 2,2¢-Biimidazoles 3a–d; General Procedure
A bisamidine 2a–d (1.0 mmol) was refluxed in HCO2H (5 mL) for
30 min, and then cooled to r.t. The soln was poured into ice–water,
and neutralized with concd aq NH3. The resulting precipitate was
filtered off, washed with H2O, and dried.
Anal. Calcd for C20H18N4O2: C, 69.35; H, 5.24; N, 16.17. Found: C,
68.98; H, 5.37; N, 16.23.
Synthesis 2010, No. 8, 1311–1314 © Thieme Stuttgart · New York

1314
K. Stippich et al.
PAPER
1,1¢-Bis(4-bromophenyl)-1H,1¢H-2,2¢-biimidazole(tetracarbon-
yl)molybdenum(0) (5)
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5 were obtained by heating to reflux in THF and then slowly cooling
to r.t. to give a yellow solid; yield: 83%.
IR (ATR): 3159, 3136, 2010, 1877, 1858, 1816, 1802, 1513, 1428,
820, 748 cm–1.
1H NMR (250 MHz, CD3CN): d = 2.29 (s, 6 H, CH3), 6.76 (d,
J = 8.3 Hz, 4 H, aryl-H), 7.06 (d, J = 8.3 Hz, 4 H, aryl-H), 7.12 (s,
2 H, imidazole-H), 7.29 (s, 2 H, imidazole-H)
13C NMR (63 MHz, CD3CN): d = 21.0, 123.1, 125.0, 129.6, 130.7,
133.6, 135.4, 138.7
MS (EI): m/z (%) = 313 (100), 223 (8), 91 (4), 28 (15)
MS (ESI): m/z (%) = 651 (87), 337 (100), 315 (26)
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1EZ, UK [fax: +44(1223)336033 or email:
Crystal Structure Determination
The intensity data for the compound were collected on a Nonius
KappaCCD diffractometer using graphite-monochromated Mo-Ka
radiation. Data were corrected for Lorentz and polarization effects,
but not for absorption effects.12,13 The structure was solved by direct
methods (SHELXS),14 and refined by full-matrix least-squares
techniques against Fo2 (SHELXL-97).15 All hydrogen atoms were
included at calculated positions with fixed thermal parameters. All
nonhydrogen atoms were refined anisotropically.15 XP (Siemens
Analytical X-ray Instruments, Inc.) was used for structure represen-
tations.
Crystal Data for 3b:16 C18H12Br2N4, Mr = 444.14 g·mol–1, light
brown prism, size 0.05 × 0.05 × 0.04 mm3, triclinic, space group Pi,
a = 8.6364(4), b = 9.1538(3), c = 10.9804(4) Å, a = 84.110(2),
b = 78.949(2), g = 77.527(2)°, V = 830.16(6) Å3, T = –90 °C,
Z = 2,
r
calcd. = 1.777 g·cm–3,
m
(Mo-Ka) = 48.89 cm–1,
F(000) = 4,365,774 reflections in h(–11/10), k(–11/11), l(–14/14),
measured in the range 1.89° £ q £ 27.49°, completeness
q
max = 99.3%, 3773 independent reflections, Rint = 0.0231, 2950 re-
flections with Fo
> 4s(Fo), 218 parameters, 0 restraints,
R1obs = 0.0346, wR2obs = 0.0775, R1all = 0.0519, wR2all = 0.0841,
GOOF = 1.015, largest difference peak and hole: 0.371/–0.688 e Å–3.
Crystal Data for 5:16 C24H18MoN4O4, Mr = 522.36 g·mol–1, yellow
prism, size 0.05 × 0.05 × 0.04 mm3, monoclinic, space group P2/c,
a = 12.9060(5), b = 13.1590(6), c = 15.8520(5) Å, b = 122.520(3)°,
V = 2270.03(15) Å3, T = –90 °C, Z = 4, rcalcd. = 1.528 g·cm–3, m
(Mo-Ka) = 6.16 cm–1, F(000) = 1056, 22201 reflections in h(–16/
16), k(–15/17), l(–20/18), measured in the range 1.87° £ q £ 27.48°,
completeness
qmax = 99.9%, 5193 independent reflections,
Rint = 0.1108, 3316 reflections with Fo > 4s(Fo), 301 parameters, 0
restraints, R1obs = 0.0425, wR2obs = 0.0807, R1all = 0.0957,
wR2all = 0.0935, GOOF = 0.981, largest difference peak and hole:
0.640/–0.981 e Å–3.
deposit@ccdc.cam.ac. uk].
Acknowledgment
R.K. thanks the Hans-Böckler-Stiftung for a scholarship.
Synthesis 2010, No. 8, 1311–1314 © Thieme Stuttgart · New York